1. Field of the Invention
The present invention relates to a pump actuation motor for use in a vehicle brake hydraulic control apparatus.
2. Description of the Related Art
In a brake hydraulic control apparatus for use in a vehicle, for example, an antilock braking system, a pump is provided in a hydraulic pressure circuit, which is connected to reservoirs, so as to return brake fluid, which is reserved in the reservoirs, to a brake master cylinder. This pump is actuated by a motor to thereby return brake fluid to the master cylinder.
The configuration of this pump actuation motor is such that a drive motor is configured so that an eccentric shaft side part of a drive shaft is rotatably supported at a side of a pump unit in a cantilever-like manner, as described in JP-A-10-892238, and so that the other end side part of the drive shaft is inserted into a cup-like motor casing and provided with a rotor, a collector (that is, a commutator), and a brush. The other end side part of the drive shaft is rotatably supported by fitting a ball bearing into a concave part that is formed by causing the bottom part of the motor casing to outwardly expand. Further, the rotor is provided by winding an armature winding around a core, which is fitted into the drive shaft, through an insulator. The insulator is placed nearly in series with the ball bearing into which the other end side part of the drive shaft is fitted.
The pump actuation motor disclosed in JP-A-10-89238 is configured so that the other end side part of the drive shaft of the motor is rotatably supported by the ball bearing fitted into the concave part, which is formed by outwardly expanding the bottom part of the motor casing, and that the insulator is placed nearly in series with the ball bearing because the clearance between the rotor and the ball bearing should be maintained. Thus, the drive shaft is lengthened. Consequently, there has been a fear that vibrations of the rotor may occur at actuation of the motor, or during an operation of the motor.
Further, the drive shaft is rotatably supported on the pump unit side in a cantilever-like manner. Thus, the length of the rotor side of the drive shaft should be shorten as much as possible. Consequently, an occurrence of a vibration of the rotor can be restrained by rotatably supporting the bearing part at a place that is close to the center of gravity of the rotor. Moreover, the miniaturization of ball bearing is enabled.